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Quantum chemical study of bis(L- histidinato)copper(II) as an isolated complex

L-histidine can bind to copper(II) in glycine-like (G), histamine-like (H), and imidazole-propionic acid-like (I) coordination mode, by three potential donor atoms for binding to copper(II), that is, imidazole imido nitrogen, amino nitrogen, and carboxylato oxygen. Numerous experimental studies of bis(L- histidinato)copper(II) have reported several coordination modes to coexist in aqueous solutions, but without providing complete structures. To get better understanding of the relative stability of all possible copper(II) coordination modes and conformations of isolated cis- and trans-bis(L-histidinato) copper(II), we have completed a conformational analysis of the title complex in vacuo in an exhaustive effort by using quantum chemical B3LYP method and LanL2DZ{; ; D95v+(d)}; ; basis set. The analysis resulted in 83 minima, with 6 cis- and 5 trans- coordination modes, in the following sequence of modes: 37 GG, 13 IG, 17 HG, 5 HH, 7 II, 1 HI, and three special cases: two six- coordinate structures and one trigonal bipyramidal structure. The most stable isolated conformer has a trans-GG coordination.

copper; L-histidine; B3LYP; coordination mode; conformational analysis

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